The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that the prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.
A problem with conveyor belt systems is that they can be subject to rips or tears, poor tracking due to poor loading, and/or bearing failures of pulleys and idlers which in turn effects their operation and in particular, their ability to carry product. In industries such as mining, failure of a conveyor belt systems can have a large impact on the overall operation of the mine. It is therefore desirable to ensure that rips and poor tracking in conveyor belts are identified as rapidly as possible to minimise their impact. A number of belt rip detection systems have been proposed.
U.S. Pat. No. 6,032,787 describes a conveyor belt condition monitoring system having a signal emitter for emitting at least one detectable signal disposed on one side of a conveyor belt, a signal receiver for receiving the detectable signal disposed on the opposite side of the conveyor belt, and a controller for controlling the emission of the at least one detectable signal and for monitoring the extent of blockage and/or transmission of the detectable signal by the conveyor belt.
Similarly, U.S. Pat. No. 5,994,712 describes a belt flaw detector having a light source for exposing the surface of the conveyor belt to radiation and a sensor for detecting transmitted radiation to warn of a flaw in the belt.
Rip detection systems of this form therefore typically require detection to be performed over the entire belt surface, which can require extensive detection systems and lead to complex signal processing requirements.
U.S. Pat. No. 5,133,448 describes a method of detecting a tear in a conveyor belt by using pivotable arms biased against the sides of the belt. Each arm is connected to a variable resistor connected into an electronic circuit so that when there is a tear in the belt, the arm will pivot inwardly causing the resistance of its associated resistor to change. This change is processed by the circuit to generate a signal which may be used to interrupt electric power to an electric motor driving the belt.
In this instance however the belt can shift on the supporting rollers leading to false rip detection, which in turn can lead to unnecessary shutting down of the conveyor belt. Additionally, not all forms of rip are evident solely by detecting the belt edge position.
U.S. Pat. No. 4,447,807 describes a system using antennas embedded within a conveyor belt. Signals are applied to the antennas as they move past a rip detector station to detect rips in the conveyor belt.
Similarly, U.S. Pat. No. 4,646,912 describes a rip detector system having electrically conductive antennae imbedded in the conveyor and spaced along the direction of movement of the belt and extending from edge to edge of the belt for carrying signals thereacross.
It will be appreciated that rip detection systems of this form require antennas to be embedded within the conveyor belt, which leads to a corresponding increase conveyor belt cost. Furthermore, such systems will only detect a rip if it intercepts one of the antennae, which may not occur for example in the case of edge rips and longitudinal rips of a short length.